# Basic set theory question

1. Oct 3, 2004

### semidevil

ok, find the intersection of i=1 to infinitie of A(i).

A(i) = [0, to 1/i].

I dont understand what it is asking. what do they mean to find the intersection of that?

and what if A(i) = [0, 1/n)

2. Oct 3, 2004

### phoenixthoth

To use mathematicasque notation, Intersect[A(i), {i,1,oo}] is the set of all points in each A(i). There's only one point in all A(i)'s: 0. Therefore the intersection is {0}. Same with the second one. But if they made it (0,1/i) then it would be empty.

3. Oct 3, 2004

### e(ho0n3

Do you mean:

$$\bigcap_{i=1}^{\infty} A(i)$$

where A(i) = [0, 1/i]? Wouldn't the answer be {0}?